A method is known from German Patent Application No. DE 116 09 922 in which the secondary air pump is checked on the basis of a response to a signal change of a lambda sensor situated in the exhaust gas of the internal combustion engine. Provided are an increase in the exhaust gas mass flow rate and a simultaneous switch-on of the secondary air pump. Due to the increased oxygen portion in the exhaust gas, the switch-on of the secondary air pump results in a signal change of the lambda sensor which in turn causes a response of a lambda controller of the engine control which carries out enrichment of the air-fuel mixture supplied to the engine. The increase in the exhaust gas mass flow rate may be achieved, for example, due to deteriorating efficiency of the engine, for example, by retarding the ignition of an externally ignited engine, by increasing the idle speed, or by connecting additional loads. If a response of the lambda controller is able to be determined, the secondary air pump is considered to be working correctly.
A further method for operating a secondary air pump is known from German Patent No. DE 199 52 836 in which an evaluation of the secondary air pump's operational performance is provided. The evaluation takes place based on the air-fuel mixture supplied to the engine, on the measured oxygen content of the exhaust gas, and on the measured air mass flow flowing to the engine.
German Patent Application No. DE 199 63 902 describes a method for operating an internal combustion engine, in which the focus is on a diagnosis of a catalytic converter. An increase in the hydrocarbon portion in the exhaust gas and simultaneously an increase in the secondary air result in an exothermic reaction in the catalytic converter. Based on the temperature control in the catalytic converter, it may be concluded that an increase in the secondary air has actually taken place and that the secondary air pump is working correctly.
A method and a device for monitoring the operational performance of a secondary air system of an internal combustion engine is known from German Patent Application No. DE 102 05 906 in which the electric operating current of the secondary air pump is analyzed. The secondary air pump may be operated using a variable power which is predefined within the scope of an electrical clocked operation. The electric operating current must lie within a predefined tolerance range, the tolerance range being a function of the pulse duty factor of the clocked operation. Moreover, the atmospheric pressure or the exhaust gas back-pressure may be taken into account. The operating voltage of the secondary air pump's electro motor may additionally be taken into account when predefining the tolerance range.
An object of the present invention is to provide a method for operating an electro motor-driven secondary air pump which makes easy adjustment of the secondary air flow rate and diagnosis of the secondary air system possible.